Generally, a conventional vehicle seat apparatus includes a lower rail and an upper rail. The lower arm is for fixing on a floor of a vehicle and is attached to a seat cushion for supporting the same. The upper arm, which supports a seat back, is pivoted by a hinge pin to a rear portion of the lower arm to rotate about the pin. A reclining apparatus is provided between the lower arm and the upper arm for restricting and allowing the upper arm to rotate.
While a passenger sits on the above-described vehicle seat apparatus, if the vehicle is impacted from the rear by another vehicle or object (hereinafter, this is referred to as a rear-end collision), the resulting rear-end collision impact load is transmitted to the seat back to receive. The impact load on the seat back is in the direction of an arrow F1, thereby causing the lower arm generate a bending moment in the direction of an arrow F2 in FIG. 1.
In order to absorb impact energy from the rear-end collision, for example, JP-2003-335162-A illustrates a vehicle seat in which a rear portion of a lower arm positioned beneath a reclining apparatus is provided with a frangible portion which is in the form of a folded offset configuration for being subject to deform upon receipt of force. The frangible portion when being deformed provides an advantage to absorb an amount of energy when the vehicle is rear-ended. However, the deformation of the frangible portion may cause the seat back to rotate or tilt excessively.
In order to avoid the excessive tilt of the seat back upon rear-end collision, one proposal is to make the lower arm more rigid for preventing an easy deformation thereof upon receipt of rear-end collision impact transmitted to the lower arm via the reclining apparatus. For enhancing the rigidity or strength of the lower arm, say, the lower arm has to be of higher section modules by reducing, bead-forming, or flange-forming, resulting in that the lower arm becomes too complex in shape to form, which leads to increase the production cost.
The present invention has been made in view of the above circumstances, and provides a vehicle seat apparatus in which the load exerted by the force applied at the rear-end collision is shared by the entire frame of the seat apparatus to prevent the excessive load from being exerted on the lower arm.